MR. GEORGE MASSEE ON THE THELEPHORER. 111 
in some way to neutralize, to a great extent, the epinasty of the 
plant ; whereas when growing on the side of a small prostrate 
branch, where the antagonistic flat surface is reduced to a 
minimum, the plant often becomes free soon after the commence- 
ment of growth, the free horizontal portion still continuing to 
develop in a more or less circular manner, which results in a 
structure that can be understood by comparing it to a reniform 
leaf attached by a short flat petiole to the branch, the lamina 
being free, more or less depressed in the centre, and incurved at 
the margin (Pl. XLV. fig. 3). This stage illustrates the origin of 
a central stem and umbrella-shaped pileus, which is perfected in 
(d) by the two lateral lobes becoming united, which results from 
the plant growing from a point where it is free to expand equally 
on every side from a short stem-like base (Pl. XLV. fig. 4). In 
some instances in the (d)-type the pileus remains solid and sur- 
rounded on all sides with the hymenium, as in Clavaria. 
It is not to be understood that every Stereum will show the 
sequence sketched above if placed consecutively in the required 
position. Some plants may be met with illustrating the (a)- 
phase in almost every conceivable direction. The point to be 
kept in view is the fact that departures from the (a)-type are 
common, and can be seen in all cases to bear a distinct relation 
to the direction of the substratum, as described above. Passing 
to the highest order of the Hymenomycetes, the Agaricinee, we 
meet with the same sequence of sporophore development. In 
the genus Pleurotus, such simple stemless species as P. applicatus, 
Batsch, illustrate the (a)-type, being attached to the substratum 
by the barren surface with the hymenium uppermost. P. hyp- 
nophilus, Berk., and P. chioneus, Pers., follow the (b)-type; P. 
ostreatus, Fr., the various stages of (c) ; while P. dryinus, Pers., 
passes through every condition of (c) to the highest condition of 
(d). Here, again, within the range of a single genus, we have a 
repetition of what has been already described as occurring in the 
Thelephores, and also the result of similar external influences 
modifying in various ways the inherent epinastie tendency. 
Sporophore evolution, as already described, is not only charac- 
teristic ordinal development, but where the orders are further 
differentiated into tribes, each tribe illustrates the same sequence, 
and, further, the same idea runs through numerous large genera 
belonging to the various orders. In 
The character of primary importance in distinguishing the 
